This invention relates to a dimmer apparatus of the type wherein a transistor for controlling a lamp to be dimmed is protected when the lamp becomes short-circuited.
Various dimmer apparatus have been developed and widely used so far. In such conventional dimmer apparatus, the resistance of a variable resistor is varied to change the duty ratio of an oscillation circuit which switches an output power transistor on and off to cause a lamp load to flicker in order to effect dimming of the lamp.
If such a lamp becomes short-circuited by some cause, an output power transistor may be broken by an excessive current. Therefore, such conventional dimer apparatus are designed to prevent destruction of an output power transistor by interrupting a possible excessive current by means of a thin track on a printed circuit board or the like when a lamp becomes short-circuited.
However, such conventional dimmer apparatus have a drawback that once the thin track is broken, a dimmer apparatus will no longer operate unless it is repaired, for example, by replacing a circuit board.